Process for the production of synthetic penicillins



United States Patent ,Ofilice 3,080,356 PatentedMar. 5, 1963,

and is particularly concerned with processes for the preparation of. a-a-mino-substituted penicillins.

Incopending applications there are described and claimed the preparation of amino-substituted penicillins by the reaction of 6-aminopenicill'anic acid with the mixed anhydride of an ot-carbobenzyloxyamino-substituted car.- boxylic acidand analkyl chloroformate followed by the hydrogenolytic removal of the carbobenzyloxy grouping from. the resulting penicillins. These penicillins included arninopentylpenicillin, a-aminoheptylpenicillin, a-aminocyclohexylmethylpenicillin, a-amino B phenylethylpenicillin, a-amino-fi-I'vindolylethylpenicillin, ot-aminobenzylpenicillin, a-amino-p-methoxybenzylpenicillin, a-aminop-chlorobenzylpenicillin, a-aminol -naphthylmethylpenicilliu, and a-amino-2-furylmethylpenicillin. It is understoodithat reference tothese penicillins is intended to include both their free acid form and their salts, including metallic salts such as sodium, potassium, calcium, and aluminum, the ammonium salt and substituted ammonium salts such as salts of trialkylamines, including triethylamine, procaine, dibenzylamine', N-benzyl-beta-phenethylamine, l-ephenamine, N,N'-dibenzylethylenediamine, dehydroabietylamine, N,N-bisdehydroabietylethylenediamine, N-(lower)alkalpiperidines, e.g. N-ethylpiperidine, and other amines which have been used to formsalts with benzylpenieillin. Also included are easily hydrolyzed esters which are'converted to the free acid form by chemical or enzymatic-hydrolysis.

This prior process has a number of disadvantages, including the fact that the mixed 'anhydride is difficult to prepare and that thehydrogenationstep requires the use ofilarge amounts of-an' expensive rare metal catalyst.

It. is the object of the present invention to provide a process for the preparation of these penicillins' which overcomes the above mentioned disadvantages;

Accordingly, the present invention provides a process for: the preparation of penicillin" of the general formula:

preferably (lower)'alkyl, aralkyl [i.e., phenyl(lower')- alkyl, includingbeuzyl, a-andfl-phenethyl, and wand 8- and 'y-phenylpropyl, etc. andthe same groups substituted once or twice with halogen, alli'oxy, phenoxy, or alkyl],

heterocyclic groups such as 3-indolylmethyl, 2-thienyl and Z-furyl [all of which. may be'. substituted in the manner set forth above for aralkyl], l-naphthyl, Z-naphthyl and phenyl [all three of, which may be substituted in the manner set forth above fo'raralkyl]. The term (lower)alkyl as used herein means both straight and branched chain aliphatic hydrocarbon, radicals having from one to ten carbon atoms such asmethyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, amyl, hex-yl; 2"-ethylhexyl, heptyl, decyl; etc. In the'preferred embodiment, R is phenyl.

'The neutral salts of -aminopenicillanic acid includes those with metals and with tertiary hydrocarbonyl amines, e-.g;, N-ethyl piperidine or' tertiary aliphatic amines such as triethylamine. Tertiary hydrocarbonyl amines are compounds having the formula wherein the R groups; contain only the elements carbon and hydrogen and include compounds such as=v pyridine and N-ethylpiperidine as well as compounds such as trialkylamines and dimethylaniline.

The present invention thus includes within its scope a process; for the preparation ofa-compoundselected from the group consisting. of. a penicillin and salts thereof, said penicillin having the formula wherein R is a member selected from the group consisting of hydrogen; (lower)'alkyl, phenyl, halophenyl, (lower)- alko'xyphenyl, phenoxyphenyl', benzyloxyphenyl, t'rifiuoromethylphenyl; nitrophenyl', acylaminophenyl, (lower)- alkylphenyl, phenylflower) alk-yl, halophenylflower) alkyl, (lower)alkoxyphenylflower)alkyl, phenoxyphenylflbwer)all' yl, benzyloxyphenylflower)alkyl, trifluoromethylphenyl(lower) alkyl, nitrophenyl(lower)'alkyl, acylaminophenyl (lower) alkyl, (lower) alkylphenyl (lower) alkyl, naphthyl, halonaphthyl, (lower) alkoxynaphthyl, phenoxynaphthyl, benzyl'oxynaphthyl, trifluoromethylnaphthyl, nitronaphthyl; acylaminonaphthyl, (lower)alkyl'naphthyl, 3- indolylmethyl, thienyl and furyl which comprises mixing atleast one stoichiometric equivalent of a member selected from the group consisting of G-aminopenicilltrni'c acid' and neutral salts thereof withla compound havingthe formula wherein R has the meaning set forth above and wherein X and Y are each members selected from the group consisting of oxygen and sulfur andatvleastwone is oxygen and a tertiary hydrocarbonyl amine in a substantially anhydrous inert solvent below about 40 C. for at least thirty minutes an'dthen recovering-said compound.

A preferred embodiment of the present invention is a process for the preparation of a compound selected from es the group consisting of a penicillin and salts thereof, said penicillin having the formula NH; N

which comprises mixing at least one stoichiometric equivalent of a member selected from the group consisting of 6-aminopenicillanic acid and neutral salts thereof with a compound having the formula wherein X and Y are each members selected from the group consisting of oxygen and sulfur and at least one is oxygen and a tertiary hydrocarbonyl amine in a substantially anhydrous iner-t solvent and then recovering said compound.

The basic condensing agent acts as an acid acceptor In the anhydride (II) X and Y may be oxygen or sulfur; in the form of the present invention in which both X and Y are oxygen the compounds are known as Leuchs anhydrides.

The intermediate penicillin (III) formed during the reaction decomposes spontaneously, or by treatment with an acid, to the desired penicillin (I). The intermediate,

penicillin (III) is not isolated and in many cases has only a transient existence.

The preferred acid acceptor is 2:6-lutidine but any tertiary hydrocarbonyl amine, e.g. triethylarnine, pyridine or the picolines, may be used.

The Leuchs anhydrides are extremely unstable compounds and when using these compounds it is essential to use nonaqueous solvents, e.g. dimethylformamide, methylenechloride, and to carry out the reaction at a low temperature, e.g. -30 to 50 C. It is preferred to use the calcium salt of 6-aminopenicillanic acid in this reaction as it is more soluble in dimethylformarnide than are the other salts of d-aminopenicillanic acid.

In an alternative form of the, present invention the monothio analogues of die Leuchs anhydricles are employed. The structure of these compounds is uncertain and is either d An adv ntage of the use of the monothio analogues is that being more stable to water and to bases than the Leuchs anhydrides they will react with a neutral salt of 6-arninopenicillanic acid, e.g. the sodium salt, in aqueous.

acetone solutions at room temperature, i.e. below about 40 C.

The compounds formed by the process of the present invention are of value as antibacterial agents, as nutritional supplements in animal feeds, as agents for the treatment of mastitis in cattle, as therapeutic agents in poultry and animals, including man, in the treatment especially of infectious diseases caused by Gram-positive and Gram-negative bacteria and as agents for the sterilization of typhoid carriers.

The penicillins of the present invention exist in epimeric forms and it will be understood that the invention includes such forms.

At the conclusion of the reaction, the products are isolated by lyophilisation. In those cases where Leuchs anhydn'des have been used, the product obtained after lyophilisation is digested with water and filtered to re move polymeric impurities and the filtrate is then once again evaporated to dryness in vacuo (bath temperature 30).

if necessary, the products obtained after lyophilisation may be redissolved in water, acidified to pH 2, the insoluble impurities removed by filtration and the filtrate adjusted to pH 7 using aqueous sodium bicarbonate solution. The resulting solution is then evaporated to dryness in vacuo (bath temperature 30). Dilute sulfuric acid (1 N) was used for the acidification when calcium G-aminopenicillanate was used and dilute hydrochloric acid (1 N) was employed in the case of sodium 6-amino penicillanate.

As a final purification process the lyophilised material 'may be absorbed on and eluted from an anion exchange resin following the procedure of Belgian Patent 569,728 for the purification of 6-arninopenicillanic acid.

6-aminopenicillanic acid is prepared according to Batchelor et al. (Nature 183, 257, 258, January 24, 1959) or Belgian Patent 569,728.

The following examples illustrate the invention:

EXAMPLE I Preparation of a-Aminobenzylpenicillin A solution of 4-phenyloxazolid-2:S-dione (0.44 g.) in dry dimethylformamide (8 ml.) was cooled to 30 C. and added during 5 mins., to a well-stirred solution of the calcium salt of 6-aminopenicillanic acid (0.8 g., prepared by adding calcium carbonate to a suspension of 6-aminopenicillanic acid in water) in dimethylformamide (25 ml.) and 2:6-lutidine (0.3 g.) also cooled to 30 C. The stirring was continued at this temperature for 5 hrs. The resulting clear solution was allowed to warm up to room temperature, water (10 ml.) added and stirred for a further 15 mins., at room temperature. The solution was evaporated to dryness in vacuo (bath temperature 30 C.) and the residual solid triturated with dry ether to give the crude calcium salt of cit-aminobenzylpenicillin (0.64 g., 51%). In order to remove some insoluble polymeric impurities, it was redissolved in water, filtered and the aqueous solution once again evaporated to dryness in vacuo (bath temperature 30 C.). Paper chromatography showed that the amount of this penicillin relative to unreacted 6-aminopenicillanic' acid was approximately in the ratio of 5:1. 7 4-phenyloxazolid-2:S-dione (65%) was prepared by cyclisation of N-carbobenzyloxy-DL-a-aminophenylacetic acid in the presence of acetic anhydride and thionyl chloride as described by Farthing (J. Chem. Soc., London, 1950, 3213) and was obtained as pale yellow microprisms, MP. 94 C. (decomp) Leuchs and Geiger (Ben, 1908, 41, 1722) quote MP. C. (decomp.).

abscissa EXAMPLE 2 Preparation" of a-Aminobenzylpenicillin A solution of 4-phenylthiazolid-2:5 dione (.7.9 g.) in acetone (190 ml.) was added dropwise during'l hour'to' a well-stirred solution of the sodium salt of 6-aminope'nicillani'c acid (10 g1) and 2:6-luti'dine (4.4 g.) in water (170 ml.) at C. Duringthe a'dition; a'precipitate'wa's observed to separate and after the addition was complete,

the reaction mixture was stirred for 0.5 hour at 0 C. The cooling bath was removed and the contents allowed to warm to room temperature when a homogenous solution resulted. The stirringwa's' then continued for 3 hours at room temperature. At the end of this period, acetone was removed under reduced pressure (bath temperature not greater than 30 C.) and final evaporation of the aqueous solution in vacuo' (bath temperature 30 C.) gavea" gummy solid. This was dried in vacuo (1' mm.) and triturated with dry ether to give the crude sodium salt of e-aminobenzylpenicillin (14.8 g.).

The 4-phenylthiazolid-2:5dione required for the above reaction was prepared by two routes:

(a) Cyclisation of N-(thiocarbethoxy)-DL-a-aminophenylacetic acid (24 g. in'dr benzene (150 ml.) in the presence of phosphorus trichl ride (18 ml.) by analogy with Aubert et al. (J. em. oc., London, 1951, 2195) gave colourless needles of 4-phenylthiazolid-2:5-dione (14 g.) M.P. 132 C., after crystallisation from chloroform/light petroleum (40-60 C.). (Found: C, 55.3; H, 4.0;. N, 7.3; S, 16.4. C H O NS-requires C, 56.0;.H, 3.6; N, 7.3; S, 16.6%.)

The N-thiocarbethoxy compound was prepared by reaction of D L-ot-aminophenylacetic acid (40 g.) with ethyl ethoxydithioformate (40 g.) inboiling, aqueous ethanolic potassium hydroxide solution for 18 hours as described by Aubert et al. (loc. cit.) to give N-(thiocarbethox-y)-DL-gx-'amin'ophenylacetic acid (44. g., 70%) ascolourless microprisms, MB. 107 C.,. on crystallisation from light petroleum (B.P. 40-60 C.)/chloroform. (Found: C, 54.5; H, 5 .3; N,- 5.6-; S, 13.0. Ci H OgNS requires C,- 55.2; H, 5.4; N, 5.9; S, 13.4%.)

Ethyl ethoxydithioformate was prepared by reacting potassium ethyl xanthate with ethyl bromide as described by-Aubert etal., (loo; cit.) and was used without further purification.

(b) Solutions of 10% aqueous sodium hydroxide (29 ml.) and of ethyl chlorothioformate (9.1 g.) in dry toluene (6 ml.) were simultaneously added to a wellstirred solution of DL-ot-aminophenylacetic acid (11 g.) in 10% aqueous sodium hydroxide (29 ml.) at 0 C. during mins. When the addition was complete, the reaction mixture was stirred for 1.5 hours at room temperature. The whole was then added with stirring to excess 5 N-hydrochloric acid and the crude reaction product was purified by treatment with aqueous sodium bicarbonate solution followed by acidification to yield N-(thiocarbethoxy)-DL-ot-aminophenylacetic acid (10.4 g., 60%) MP. and mixed M.P. 107 C., as colourless microprisms on crystallisation from light petroleum (B.P. -60" C.) chloroform.

Ethyl chlorothioforma-te was obtained in 53% yield as a pale yellow lachrymatory liquid, B.P. 55-57 C./ 18 mm, by the reaction of sodium ethoxide with thinphosgene in dry benzene according to the procedure described by Rivier and Richard (Helv. chim. Acta., 1925, 8, 490).

Aditional information on N-carboxy-a-amino acid anhydrides with regard to their preparation and reactions is to be found on pages 136160 of Advances in Protein Chemistry, vol. VI, 1951, Academic Press, Inc., New York, N.Y., and in the references cited therein.

While in the foregoing specification various embodiments of this invention have been set forth and specific details thereof elaborated for the purpose of illustration, it will be apparent to those skilled in the art that this T er )Ialkanoylaminonaphthyl,

invention" is susceptible to" other" embodiments and that many of these details may be'varied widely without d'e-' parting from the basic conceptan'd spirit of the invention.

Weclaim: 1. A process for the preparation of a'penicillin, said penicillin having the formulawherein R'is a memberselected' from-the group consisting'o'f hydrogen; (lower)alkyl', phenyl, halophenyl, (lower)alkoxyphenyl, phenoxyphenyl, benz-ylbxyphenyl, "trikyl, trifluoromethylphenyl(lower)alkyl, nitrophenyl(lower) alkyl, (lower) alkanoylaminophenyl (lower) alkyl, (lower) alkylphenyl' (lower) alkyl,. .naphthyl, halonaphthyl, (loweflhlkoxynaphthyl, phenoxynaphthyl, benzyloxynaphthyl, trifiuoromethylhaphthyl, nitronaphthyl', (low- (Ilower)falkylnaphthyl,. indolyhnethyl, thienyl' and furyl' which comprises mixinga member selected from the group consisting. of 6-aminopenicillanic acid and neutral salts thereof" with a compound having the formula wherein Rxhas the meaning set forth above and whereinX and Y are each members selected from thegroup consisting of oxygen and sulfur and at least one is oxygen and a basic condensing agent in a substantially anhydrous inert solvent.

2. A process for the preparation of a penicillin, said penicillin having the formula /s\ /CH: R-CHC-NH-OHCH C-GH! NH, (l'J-NCHCOOH wherein R is a. member selected from the group consisting of hydrogen, (lower) alkyl, phenyl, halophenyl, (lower)- alkoxyphenyl, phenoxyphenyl, benzyloxyphenyl, trifiuoromethylphenyl, nitrophenyl, (lower alkanoylaminophenyl, (lower) alkylphenyl, phenyl(lower) alkyl, halophenyl(lower) alkyl, (lower) alkoxyphenyl (lower) alkyl, phenoxyphenyl(lower)alkyl, benzyloxyphenylflower)alkyl, trifiuoromethylphenyl (lower) alkyl, nitrophenyl(lower)alkyl, (lower) alkanoylaminophenyl (lower) alkyl, (lower) alkylphenylflower) alkyl, naphthyl, halonaph-thyl, (lower)alkoxynaphthyl, phenoxynaphthyl, benzyloxynaphthyl, trifiuoromethylnaphthyl, nitronaphthyl, (lower)alkanoylaminonaphthyl, (lower)alkylnaphthyl, 3-indolylmethyl, thienyl and furyl which comprises mixing at least one stoichiometric equivalent of a member selected from the group consisting of 6-aminopenicillanic acid and neutral salts thereof with a compound having the formula R-OH-C NH-C wherein R has the meaning set forth above and wherein X and Y are each members selected from the group con sisting of oxygen and sulfur and at least one is oxygen 7 and a tertiary hydrocarbonyl amine in a substantially anhydrous inert solvent below about 40 C. for at least thirty minutes and then recovering said compound.

3. A process for the preparation of a penicillin, said penicillin having the formula /S\ /CH: CHC-NHCHCH OC}I3 d m (J -1 I(';H000H which comprises mixing at least one stoichiometric equivalent of a member selected from the group consisting of 6-arninopenicillanic acid and neutral salts thereof with a compound having the formula wherein X and Y are each members selected from the group consisting of oxygen and sulfur and at least one is oxygen and a tertiary hydrocarbonyl amine in a substantially anhydrous inert solvent and then recovering said compound.

4. A process for the preparation of a penicillin, said penicillin having the formula which comprises mixing at least one stoichiometric equivalent of a member selected from the group consisting of G-aminopenicillanic acid and neutral salts thereof with a compound having the formula wherein R is (loweryalkyl which comprises mixing at least one stoichiometric equivalent of a member selected from the group consisting of G-aminopenicillanic acid and neutral salts thereof with a compound having the formula NEE-(l? wherein R is (lower)alkyl and wherein X and Y are each members selected from the group consisting of oxygen and sulfur and at least one is oxygen and a tertiary hydrocarbonyl amine in a substantially anhydrous inert solvent below about 40 C. for at least thirty minutes and then recovering said compound.

References Cited in the file of this patent UNITED STATES PATENTS Doyle et a1 June 21, 1960 Doyle et a1. Sept. 6, 1960 OTHER REFERENCES Wertheim, Textbook of Organic Chemistry, pages 227- 228, second edition (1945). 

1. A PROCESS FOR THE PREPARATION OF A PENICILLIN SAID PENICILLIN HAVING THE FORMULA 